import React,{Component} from "react";export default class DeControlComponents extends Component {    //非受控组件 --现用现取  --一般用ref的比较多    render() {        return (            <div>                <form action='http://www.atguigu.com' onSubmit={this.handleSunmit}>                   用户名: <input ref={c => this.username = c} type="text" name="username"/>                   密码:   <input ref={c => this.password = c} type="password" name="password"/>                    <button>登录</button>                </form>            </div>        )    };    handleSunmit = (event)=>{        event.preventDefault()   //阻止表单提交        const {username,password} = this    alert(`你输入的用户名是${username.value},密码是${password.value}`)    }}